The present invention relates to a digital broadcasting channel selection apparatus and a digital broadcasting channel selection method in which a broadcasting signal on a channel selected from digital broadcasting is turned in to.
In recent years, broadcasting has been digitized, and various types of digital broadcasting such as BS (Broadcasting Satellite) digital broadcasting, cable television (CATV) broadcasting, and ground wave digital broadcasting have been developed. In the digital broadcasting, programs on a plurality of channels are broadcast, and a digital broadcasting channel selection apparatus is used in order for a viewer to select a broadcasting signal on the desired channel.
In a conventional digital broadcasting channel selection apparatus, therefore, a local oscillation signal corresponding to the center frequency of a carrier wave for a broadcasting signal is mixed with an RF (Radio Frequency) signal received through a parabolic antenna or the like to convert the RF signal into an IF (Intermediate Frequency) signal, to tune in to the broadcasting signal on the desired channel.
At this time, the local oscillation frequency of the local oscillation signal is controlled by AFT (Automatic Fine Tuning) such that the IF signal has a predetermined intermediate frequency, and PLL (Phase-Locked Loop) control is used in order to control the local oscillation frequency to a desired frequency, to tune in to a broadcasting signal having a center frequency within a lead-in range by the PLL control.
In the conventional digital broadcasting channel selection apparatus, however, the lead-in range by the PLL control is limited to a predetermined frequency range. When the center frequency of the carrier wave for the broadcasting signal is outside the lead-in range, the broadcasting signal cannot be tuned in to. For example, in CATV in the United States, the center frequency fRF of the carrier wave for the broadcasting signal may, in some cases, be shifted in a range of xc2x1300 kHz from a nominal value. The shift in the frequency is within a standard range in the CATV in the United States. When the frequency lead-in range by the PLL control is a range of xc2x1150 kHz, centered at the center frequency fRF of the carrier wave for the broadcasting signal, however, the broadcasting signal cannot be tuned in to.
An object of the present invention is to provide a digital broadcasting channel selection apparatus and a digital broadcasting channel selection method in which a broadcasting signal on a desired channel can be tuned in to even when the frequency precision of a carrier wave for the broadcasting signal is low.
A digital broadcasting channel selection apparatus according to an aspect of the present invention is a digital broadcasting channel selection apparatus for tuning in to a broadcasting signal on a channel selected from digital broadcasting, comprising selection means for selecting a channel in digital broadcasting; frequency setting means for setting a channel selection frequency corresponding to the channel selected by the selection means; tuning means for tuning in to the broadcasting signal using the channel selection frequency set by the frequency setting means; and detection means for detecting whether or not the tuning means can tune in to the broadcasting signal on the selected channel and notifying the frequency setting means of the result of the detection, the frequency setting means shifting, when the detection means detects that the tuning means cannot tune in to the broadcasting signal on the selected channel, the channel selection frequency to the high frequency side or the low frequency side.
In the digital broadcasting channel selection apparatus, the channel selection frequency corresponding to the selected channel is set, and the broadcasting signal is tuned in to using the set channel selection frequency. At this time, when it is detected that the broadcasting signal on the selected channel cannot be tuned in to, the channel selection frequency is shifted to the high frequency side or the low frequency side.
At the time of the channel selection after shifting the channel selection frequency, therefore, the broadcasting signal can be tuned in to using the channel selection frequency shifted to the high frequency side or the low frequency side. Even in a case where the center frequency of the carrier wave for the broadcasting signal on the selected channel is shifted from a nominal value and deviates from a lead-in range based on the first channel selection frequency, therefore, when the center frequency of the carrier wave for the broadcasting signal on the selected channel exists in the lead-in range after the shifting, the broadcasting signal on the selected channel can be tuned in to. As a result, even when the frequency precision of the carrier wave for the broadcasting signal is low, the broadcasting signal on the desired channel can be tuned in to.
It is preferable that the frequency setting means shifts the channel selection frequency to the high frequency side or the low frequency side, and then shifts, when the detection means detects again that the tuning means cannot tune in to the broadcasting signal on the selected channel, the channel selection frequency to the opposite side.
In this case, the channel selection frequency is shifted to the high frequency side or the low frequency side, and the channel selection frequency is then shifted to the opposite side when it is detected again that the broadcasting signal on the selected channel cannot be tuned in to. When the center frequency of the carrier wave for the broadcasting signal on the selected channel is shifted in the opposite direction to the direction in which it is first shifted, therefore, the broadcasting signal on the selected channel can be tuned in to by shifting the channel selection frequency to the opposite side.
The frequency setting means may successively shift the channel selection frequency to the high frequency side or the low frequency side until the tuning means can tune in to the broadcasting signal on the selected channel.
In this case, the channel selection frequency is successively shifted to the high frequency side or the low frequency side until the broadcasting signal on the selected channel can be tuned in to. Even when the center frequency of the carrier wave for the broadcasting signal on the selected channel is greatly shifted, therefore, the broadcasting signal on the selected channel can be tuned in to by successively shifting the channel selection frequency.
It is preferable that the frequency setting means stops an operation for shifting the channel selection frequency when the tuning means cannot tune in to the broadcasting signal on the selected channel after the channel selection frequency is shifted a predetermined number of times.
In this case, when the broadcasting signal on the selected channel cannot be tuned in to after the channel selection frequency is shifted a predetermined number of times, the operation for shifting the channel selection frequency is stopped. In cases such as a case where broadcasting on the selected channel is not performed, therefore, a channel selection operation can be stopped without being uselessly continued.
It is preferable that the digital broadcasting channel selection apparatus further comprises recording means for recording for each channel the amount of shift in the channel selection frequency corresponding to the channel, the frequency setting means recording, when the detection means detects that the tuning means can tune in to the broadcasting signal on the selected channel, the amount of shift in the channel selection frequency corresponding to the channel on the recording means as well as shifting the channel selection frequency by the amount of shift recorded on the recording means when the channel selection frequency is set in the tuning means.
In this case, when it is detected that the broadcasting signal on the selected channel can be tuned in to, the amount of shift in the channel selection frequency corresponding to the channel is recorded on the recording means, and the channel selection frequency is shifted by the amount of shift recorded on the recording means when the channel selection frequency is set. At the subsequent channel selection, therefore, the channel can be tuned in to by shifting the channel selection frequency by an amount of shift in which the channel could be selected last time. Accordingly, the desired channel can be quickly tuned in to without performing a useless channel selection operation.
The frequency setting means may record on the recording means for each channel the result of the detection whether or not the tuning means can tune in to the broadcasting signal on the selected channel.
In this case, the result of the detection whether or not the broadcasting signal on the selected channel can be selected is recorded on the recording means for each channel. For example, a viewer can be notified that when an instruction to tune in to the same channel is issued since that time, the channel cannot be tuned in to, or the channel which cannot be tuned in to at the time of an auto-channel operation for automatically raising or lowering the channel can be skipped. Accordingly, it is possible to restrain an operation for tuning in to the channel which may not be or is hardly tuned in to.
It is preferable that the tuning means converts the broadcasting signal tuned in to using the channel selection frequency set by the frequency setting means into an intermediate frequency signal and outputs the intermediate frequency signal, and the detection means detects whether or not the broadcasting signal on the selected channel can be tuned in to on the basis of the result of decoding of the intermediate frequency signal outputted from the tuning means.
In this case, the broadcasting signal tuned in to is converted into the intermediate frequency signal, and it is detected whether or not the broadcasting signal on the selected channel can be tuned in to on the basis of the result of the decoding of the intermediate frequency signal obtained by the conversion. Accordingly, it can be detected whether or not the broadcasting signal is a broadcasting signal on the selected channel using the result of the decoding, for example, various types of information included in a transport stream. Accordingly, it is possible to reliably detect not only that the channel can be merely tuned in to but also whether or not the channel tuned in to is the selected channel. As a result, even when a plurality of broadcasting signals exist in the lead-in range based on the set channel selection frequency, the broadcasting signal on the channel selected by the viewer can be reliably tuned in to.
A digital broadcasting channel selection method according to another aspect of the present invention is a digital broadcasting channel selection method for tuning in to a broadcasting signal on a channel selected from digital broadcasting, characterized by comprising the steps of setting a channel selection frequency corresponding to the selected channel; tuning in to the broadcasting signal using the set channel selection frequency; detecting whether or not the broadcasting signal on the selected channel can be tuned in to in the tuning step; and shifting, when it is detected in the detecting step that the broadcasting signal on the selected channel cannot be tuned in to, the channel selection frequency to the high frequency side or the low frequency side.
In the digital broadcasting channel selection method, the channel selection frequency corresponding to the selected channel is set, and the broadcasting signal is tuned in to using the set channel selection frequency. At this time, when it is detected that the broadcasting signal on the selected channel cannot be tuned in to, the channel selection frequency is shifted to the high frequency side or the low frequency side.
At the time of the channel selection after shifting the channel selection frequency, therefore, the broadcasting signal can be tuned in to using the channel selection frequency shifted to the high frequency side or the low frequency side. Even in a case where the center frequency of the carrier wave for the broadcasting signal on the selected channel is shifted from a nominal value and deviates from the lead-in range based on the first channel selection frequency, therefore, when the center frequency of the carrier wave for the broadcasting signal on the selected channel is in the lead-in range after the shifting, the broadcasting signal on the selected channel can be tuned in to. As a result, when the frequency precision of the carrier wave for the broadcasting signal is low, the broadcasting signal on the desired channel can be tuned in to.
It is preferable that the digital broadcasting channel selection method further comprises the steps of tuning in to the broadcasting signal again using the channel selection frequency shifted to the high frequency side or the low frequency side in the shifting step, detecting again whether or not the broadcasting signal on the selected channel can be tuned in to in the step of tuning again, and shifting, when it is detected in the step of detecting again that the broadcasting signal on the selected channel cannot be tuned in to, the channel selection frequency to the opposite side.
In this case, when it is detected again that the broadcasting signal on the selected channel cannot be tuned in to after the channel selection frequency is shifted to the high frequency side or the low frequency side, the channel selection frequency is shifted to the opposite side. When the center frequency of the carrier wave for the broadcasting signal on the selected channel is shifted in the opposite direction to the direction in which it is first shifted, therefore, it is possible to tune in to the broadcasting signal on the channel selected by shifting the channel selection frequency to the opposite side.
The shifting step may comprise the step of successively shifting the channel selection frequency to the high frequency side or the low frequency side until the broadcasting signal on the selected channel can be tuned in to.
In this case, the channel selection frequency is successively shifted to the high frequency side or the low frequency side until the broadcasting signal on the selected channel can be tuned in to. Even when the center frequency of the carrier wave for the broadcasting signal on the selected channel is greatly shifted, therefore, it is possible to tune in to the broadcasting signal on the selected channel by successively shifting the channel selection frequency.
It is preferable that the digital broadcasting channel selection method further comprises the step of stopping an operation for shifting the channel selection frequency when the broadcasting signal on the selected channel cannot be tuned in to after the channel selection frequency is shifted a predetermined number of times.
In this case, when the broadcasting signal on the channel selected after shifting the channel selection frequency a predetermined number of times cannot be tuned in to, the operation for shifting the channel selection frequency is stopped. In cases such as a case where the selected channel is not broadcast, therefore, a channel selection operation can be stopped without being uselessly continued.
It is preferable that the digital broadcasting channel selection method further comprises the step of recording on recording means for each channel, when it is detected in the detecting step that the broadcasting signal on the selected channel can be tuned in to, the amount of shift in the channel selection frequency corresponding to the channel, the setting step comprising the step of shifting, when the channel selection frequency is set, the channel selection frequency by the amount of shift recorded on the recording means.
In this case, when it is detected that the broadcasting signal on the selected channel can be tuned in to, the amount of shift in the channel selection frequency corresponding to the channel is recorded on the recording means, and the channel selection frequency is shifted by the amount of shift recorded on the recording means when the channel selection frequency is set. At the time of the subsequent channel selection, therefore, the channel can be tuned in to by shifting the channel selection frequency by an amount of shift in which the channel could be selected last time. Accordingly, the desired channel can be quickly tuned in to without performing a useless channel selection operation.
The digital broadcasting channel selection method may further comprise the step of recording on the recording means for each channel the result of the detection in the detecting step whether or not the broadcasting signal on the selected channel can be tuned in to.
In this case, the result of the detection whether or not the broadcasting signal on the selected channel can be selected is recorded on the recording means for each channel. When an instruction to select the same channel is issued since that time, for example, therefore, the viewer can be notified that the channel cannot be tuned in to, or the channel which cannot be tuned in to at the time of an auto-channel operation for automatically raising or lowering the channel can be skipped. Therefore, it is possible to restrain the operation for tuning in to the channel which may not be or is hardly tuned in to.
It is preferable that the tuning step comprises the step of converting the broadcasting signal tuned in to using the channel selection frequency set in the setting step into an intermediate frequency signal and outputting the intermediate frequency signal, the detecting step comprises the step of detecting whether or not the broadcasting signal on the selected channel can be tuned in to on the basis of the result of decoding of the intermediate frequency signal obtained by the conversion.
In this case, the broadcasting signal tuned in to is converted into the intermediate frequency signal, and it is detected whether or not the broadcasting signal on the selected channel can be tuned in to on the basis of the result of the decoding of the intermediate frequency signal obtained by the conversion. Accordingly, it can be detected whether or not the broadcasting signal is a broadcasting signal on the selected channel using the result of the decoding, for example, various types of information included in a transport stream. Accordingly, it is possible to reliably detect not only that the channel can be merely tuned in to but also whether or not the channel tuned in to is the selected channel. As a result, even when a plurality of broadcasting signals exist in the lead-in range based on the set channel selection frequency, the broadcasting signal on the channel selected by the viewer can be reliably tuned in to